That's not what AM said. If you introduce the planned Labour idea of limiting the maximum salary to the minimum salary in a company, then any business that pays the minimum wage to any member of staff has automatically set a ceiling on the top salary they can pay.
To increase the top salary available, they would have to raise the salary of the lowest paid employees by the same ratio. That then presumably necessitates a pay rise for all staff, otherwise what is the incentive for the extra work and responsibility of a higher level job?
Or they reorganise they company such that all the NMW staff are employed by a sub-contractor rather than them and its trebles all round again.